It is a well know "fact" that calendars increase when volatility increases. This however is the furthest thing from the truth. The back month vol has to increase by more than root time for IV to have a positive impact on the calendar. OR the front month has to decrease by more than root time. After finishing "dynamic hedging" by taleb last night I have come to the conclusion that the calendar spread is a very complex strategy. There are many factors that influence the position such as vol of vol, skew, shadow gamma/vega. It is not an easy task and is giving me some head aches. None the less I will update on here my findings.